1. Field of the Invention
The present invention relates to tools for drilling and screwing. More particularly, it relates to a combination tool for performing both drilling and screwing work operations.
2. The Prior Art
When working as a professional, or even at the home work level, workpieces consisting of wood or similar materials are generally joined by means of screws or screw-like fasteners. In order to join the pieces together without damaging them, a hole for receiving the screw is first drilled into the workpiece. Even when using so-called self-cutting screws, predrilling of a screw hole is recommended, especially when joining wood workpieces, the quality of the coupling is increased. Furthermore, if the respective screw holes are slightly recessed before the fastening means is screwed in, the fastener can be countersunk into the workpiece. Without a slight chamfering of the screw holes, the workpieces disposed directly near the fastening means can be damaged, or at least become visually impaired.
Screwing tools or reversible drilling machines are increasingly used for facilitating the tightening and loosening of screws or screw-like fasteners. However, it is difficult, and sometimes annoying, to be required to manipulate two or three tools. These tools are generally drills, various screwing tools and, if need be, a sinking tool in order to complete the work operations, which have to be carried out directly one after the other.
For solving this problem, it is proposed in DE-OS 3 938 244 to use a special adapter that enables the user to change between a drill and a screwing tool without having to use the chuck normally used in connection with drilling machines. Accordingly, the published reference describes a quick-change attachment. The disclosed solution facilitates the handling of the drilling machine with some work operations; however, the user continues to be forced to keep several different tools available for carrying out all of the sequential work operations.
It has been proposed in DE-OS 2 620 176, as well as in DE-PS 2 660 357, which is branched from the former, to connect a drilling machine with a displaceable sleeve. The displaceable sleeve can be pushed back such that the drilling insert is released. When pushed forward, the sleeve grips over the head of a screw like a nut, and the respective screw can subsequently be screwed in. As a further development of this solution, DE-OS 3 008 394 describes another screwing sleeve, which also can be operated in connection with a percussion drilling machine.
The aforesaid solutions have drawbacks in that they cannot be applied with conventional drills or screwing tools, but require a special driving machine. The displaceable screwing sleeve solution requires the drilling machine to be permanently equipped with an excessively protruding front attachment which is troublesome in practical use.